Severiano Ballesteros was last night resting in a Madrid hospital after doctors performed a biopsy on the brain tumour detected last week. The procedure will determine whether the tumour is benign or malignant, but no result has so far been made public.

Ballesteros has spent the past 10 days having tests after being taken to hospital following a fainting fit and dizzy spells. He has had several bouts of illness since retiring from competitive golf last year but news of his condition nevertheless came as an unpleasant surprise to the golf world. The Spaniard is still just 51 years old, an age at which many golfers are still playing on the senior circuit.

Fellow golfers yesterday added their voices to the fans who have inundated Ballesteros with goodwill messages since he was first taken to hospital. "Seve we love you. We are all hoping that you will recover as soon as possible," his fellow Spanish golfer Miguel Angel Jiménez said.

"Seve was such a great hero of mine," said Lee Westwood, whose 1997 Ryder Cup debut was under Ballesteros's captaincy. "I never played with a more charismatic golfer, but he was not just extraordinary in the golfing sense. If you went into a room, you knew he was there even if you couldn't see or hear him. That's how big he was in his heyday and even now."

José María Olazábal, who visited him in hospital before the brain tumour diagnosis had been confirmed, said he had looked physically well. "We chatted for a good while," he said. "He was obviously concerned but he seemed on good form."

"It's very scary, shocking, and very sad," said Paul Casey. "He was one of my heroes, one of my idols. I loved the way he played. I was fortunate enough to play with him in Spain for a couple of rounds and it was just great Seve golf. He was all over the course, getting up and down from outrageous positions, which is exactly the way I remember watching him play around Wentworth and places like that. He's always been great to me and supportive and I'd like to have him around for a lot longer so I hope he gets better."

Ballesteros, in confirming the tumour on Sunday, recalled that "throughout my whole career I have been one of the best at facing obstacles on the golf course", a point made by several of his colleagues. "Seve has this positive approach," said Colin Montgomerie, "and we are willing him to recover. In the past he has been four down with nine to play and has come back, so although this is by far the biggest fight of his life, we all hope he will pull through."

Darren Clarke, who was also making his Ryder Cup debut when Ballesteros captained the Europe team at Valderrama in 1997, summed up the thoughts of many when he acclaimed Ballesteros as "among the best-loved golfers of all time, as well as one of the greatest golfers ever to have held a club".